> modify the node in-place

I consider this anti-pattern [1].

[1] https://web.archive.org/web/20070417190836/https://www.eecs....

Authors found themselves fighting with control flow graph modifications and replaced mutable graph with immutable one, modified by zippers. They achieved speed up of 11% in optimizing transformations, some of which they were unable to implement in mutable version. E.g., more complex optimizations were working faster.